A lymph node in the breast area is a small, bean-shaped organ that is part of the body’s lymphatic system. This system is a network of vessels, tissues, and organs that works in parallel with the circulatory system. Its functions involve maintaining fluid balance and serving as a major component of the immune defense system. Lymph nodes act as filtering stations for lymph fluid, a clear substance composed of white blood cells, proteins, and excess fluid collected from tissues.
What Lymph Nodes Do
Lymph nodes function as checkpoints where the body filters lymph fluid before returning it to the bloodstream. As lymph fluid passes through a node, it is scrutinized for foreign particles, pathogens, cellular debris, and abnormal cells. This filtering is accomplished by specialized immune cells housed within the node.
These organs are populated with lymphocytes (B-cells and T-cells) and macrophages. Macrophages act as scavengers, engulfing and destroying trapped material. If a pathogen is detected, the lymphocytes activate and multiply rapidly to initiate a targeted immune response. This proliferation of immune cells is why a lymph node will swell and become tender during an infection.
Where Breast Lymph Nodes Are Located
The lymphatic network of the breast is extensive, but most lymph fluid drains into specific regional groups. The most significant drainage site, receiving approximately 75% of the lymph from the breast tissue, is the Axillary Lymph Nodes located in the armpit (axilla).
These nodes are categorized into three levels based on their anatomical relationship to the pectoralis minor muscle.
- Level I nodes are situated laterally to the muscle.
- Level II nodes are directly beneath the muscle.
- Level III nodes are located medially, closer to the chest wall.
Secondary drainage pathways also exist, including the Internal Mammary Nodes, which run alongside the breastbone (sternum). Lymph fluid may also drain toward the Supraclavicular and Infraclavicular nodes, located above and below the collarbone.
Lymph Nodes and Breast Cancer Staging
The status of the lymph nodes that drain the breast tissue is considered one of the most important prognostic factors in breast cancer. Cancer cells that break away from a primary tumor often travel through the lymphatic vessels to the nearest lymph nodes, a process known as metastasis. The presence or absence of cancer cells within these nodes directly informs the cancer’s stage, specifically the “N” (Node) classification in the TNM staging system.
To determine if the cancer has spread, physicians perform a Sentinel Lymph Node Biopsy (SLNB), which is the standard of care for many patients. The sentinel node is the first lymph node or group of nodes to receive lymphatic drainage directly from the tumor site. The procedure involves injecting a tracer, such as a radioactive substance or blue dye, into the breast to locate and remove these nodes.
If the sentinel node is negative for cancer cells, it suggests the cancer has not yet spread to the rest of the lymphatic system. If the sentinel node contains cancer, the surgeon may proceed with an Axillary Lymph Node Dissection (ALND), which involves removing a larger number of axillary nodes. This procedure is performed to remove any additional disease and determine the extent of the cancer spread, though its use has become less common for patients with minimal disease in the sentinel nodes.
The number of lymph nodes that contain metastatic cancer cells, along with the size of the tumor deposits, influences the treatment plan and provides an indication of recurrence risk. The goal of assessing the nodes is to accurately predict the trajectory of the disease and tailor subsequent treatments, such as chemotherapy or radiation.
Other Reasons for Enlarged Lymph Nodes
While the connection between lymph nodes and breast cancer is a concern, the majority of lymph node swelling (lymphadenopathy) is caused by common, non-cancerous conditions. Swelling occurs when the immune cells within the node proliferate and accumulate in response to a perceived threat. This is a normal function of the immune system.
Local infections in the breast or arm, such as mastitis, a skin infection, or an injury, can cause the nearby axillary nodes to become enlarged and tender. Systemic infections, including viral illnesses like the flu, may also result in temporary lymph node swelling. A recent vaccination, particularly one administered in the arm, can also cause reactive swelling as the body mounts an immune response. Any persistent or unexplained lump should always be evaluated by a healthcare professional to determine the underlying cause.